The present invention relates generally to the preparation of actinide boride materials suitable for intermediate storage of actinide elements and, more particularly, to the use of low-temperature, solid-state metathesis reactions to prepare these materials.
Department of Energy strategy for plutonium has shifted in focus within the past decade from production and recycling to stabilization and disposal. This change results from the reduction in the nuclear stockpile and the accompanying need for plutonium disposition. Today""s strategy uses plutonium oxide as the optimum intermediate (i.e. xe2x89xa650-year) storage form, even though John M. Haschke et al. reported in xe2x80x9cReaction of Plutonium Dioxide with Water: Formation and Properties of PuO2+Xxe2x80x9d, Science 287, 285 (2000), that PuO2 slowly reacts with moisture to form hydrogen, causing numerous safety and storage concerns.
The area of actinide borides is underdeveloped, in part due to the high temperatures required to produce these materials (See, e.g., H. A. Eick and R. N. R. Mulford, J. Inorg. Nucl. Chem. 31, 371 (1969). The list of known binary thorium- and uranium-boride phases includes only ThB4, ThB6, ThB66, UB2, UB4, UB12, with little information reported on their chemical properties (See, e.g., J. J. Katz et al. The Chemistry of Actinide Elements, Chapman and Hall; New York, N.Y. (1986), pages 56, 280 and 317 for Th, U and Pu, respectively). In contrast, plutonium borides have been synthesized at lower temperatures but require the use of molten plutonium (800xc2x0 C.), which is extremely corrosive (See, e.g., H. A. Eick, Inorg. Chem. 4, 1237 (1965)), or the use of PuH3 (900xc2x0 C.) (See, e.g., R. E. Skavdahl et al., Trans. Am Nucl. Soc. 7, 403 (1964)). Plutonium borides are known to be refractory, but other properties such as chemical behavior and stability have not been evaluated. In contrast, many transition metal and lanthanide borides, such as ZrB2 (See, e.g., K. Su and L. G. Sneddon, Chem. Mater. 5, 1659 (1993) and L. Rao et al., J. Mater. Res. 10, 353 (1995)), and LaB6 (See, e.g., S. S. Kher and J. T. Spencer, J. Phys. Chem. Solids 59, 1343 (1998)), have been extensively studied and have been used as refractory materials and corrosion-resistant coatings. It is therefore expected that some actinide-boride phases will also be corrosion resistant.
During the past two decades significant advances have been made in the low-temperature synthesis of highly refractory materials (See, e.g., K. H. Wynne and R. W. Rice, Ann. Rev. Mater. Sci. 14, 297 (1984) and R. W. Rice, Am. Ceram. Soc. Bull. 62, 889 (1983)). New methods, such as molecular precursors, pre-ceramic polymers, chemical vapor deposition, sol-gel and hydrothermal syntheses, low-temperature molten salts, self-propagating high-temperature synthesis (SHS), and solid-state metathesis reactions (SSM), virtually eliminate the problems associated with slow solid-state diffusion by mixing the constituents of the ceramic at a molecular level. SHS and SSM methods have been used successfully to synthesize transition metal borides, nitrides, and oxides and actinide oxides and nitrides at low- to moderate-temperatures (See, e.g., E. G. Gillan and R. B. Kaner, Chem. Mater. 8, 333 (1996), I. P. Parkin and J. C. Fitzmaurice, J. Mat. Sci. Lett. 13, 1185 (1994), and I. P. Parkin and J. C. Fitzmaurice, New J. Chem. 18, 825 (1994)). The key to low-temperature synthesis is identification of suitable precursors that lead to ceramic materials having the desired physical characteristics described above. However, no mention is made of generating actinide borides using low-temperature SSM.
Accordingly, it is an object of the present invention to provide a low-temperature method for preparing stable actinide boride ceramic compositions from commonly available or readily prepared actinide compounds.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the Invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the method for preparing an actinide boride of an actinide element hereof includes the step of heating a mixture of a halide of the actinide element with a chosen amount of magnesium diboride such that a metathesis reaction occurs.
In another aspect of the present invention, in accordance with its objects and purposes, the method for preparing an actinide boride of an actinide element hereof includes the step of heating a mixture of an oxide of the actinide element with a chosen amount of magnesium diboride such that a metathesis reaction occurs.
In still another aspect of the present invention, in accordance with its objects and purposes, the method for preparing an actinide boride of an actinide element hereof includes the step of heating a mixture of an oxyhalide of the actinide element with a chosen amount of magnesium diboride such that a metathesis reaction occurs.
Benefits and advantages of the present invention include the conversion of already existing or readily generated actinide compounds into less-reactive, safer storage forms utilizing metathesis reactions which take place at readily attainable temperatures.